Deinked pulp has become a principal source of raw material for making paper in applications such as newsprint and tissue production. The deinking process has evolved throughout the years to provide for the removal of ink from recycled paper. In conventional paper recycling processes, deinking is carried out by converting the waste paper, such as old newspaper, old magazines and mixed office waste, to a pulp and then contacting the pulp with an alkali for pH modification and swelling of the fiber and a surfactant to stabilize the ink particles and reduce reattachment of the ink particles to the fiber. The ink particles and other impurities from the pulp fiber are then released and separated.
The current deinking processes employed in separating the ink from the fiber in waste paper include wash deinking, flotation deinking or a combination of these methods. Flotation deinking involves the interaction between the ink particles, air bubbles and the fibers. The ink particles, which are typically rendered hydrophobic by a deinking surfactant, attach to the air bubble surfaces and float upwards towards the top of the flotation device. Under typical conditions, the fiber will remain hydrophilic and will neither attach to the air bubbles nor float during the flotation process. In the case of wash deinking, the ink particles are kept well dispersed in the aqueous phase by surfactants. The ink particles are separated from the fibers by a repeated flow of water passing by the fibers through a screen. This wash deinking technology involves multiple dilution and thickening stages.
In deinking, the surfactants used are either fatty acids, synthetic surfactants such as alkoxylates or blends of these two surfactant types. Fatty acids are well known flotation agents used in both mineral and non-mineral applications. The use of synthetic surfactants such as alkylamine polyethers as deinking aids is described in U.S. Pat. Nos. 4,483,741 and 4,605,773. The use of a blend of fatty acid and alkylene oxide as a deinking agent is described in U.S. Pat. No. 4,964,949.
Another synthetic surfactant blend used in flotation deinking is a polyester obtained through the reaction between a polyalkylene glycol, carboxylic acid and/or anhydrides and saturated fatty acids, as described in U.S. Pat. No. 5,736,622.
U.S. Pat. Nos. 5,227,019; 5,225,046; 5,725,730 and 5,801,135 disclose the use of fatty acids with alkoxylated fatty alcohols in deinking. A flotation deinking method using an alkylene oxide, oil, fat and alcohol is described in U.S. Pat. No. 6,251,220.
U.S. Pat. Nos. 5,151,155 and 5,336,372 describe a deinking process wherein organically modified smectite clay is used.
U.S. Pat. No. 5,540,814 describes a method for removing ink and reducing stickies from waste paper by using cationic kaolin clay and a centrifugal cleaner.
Due to the limitations of these different deinking processes to separate the ink particles from the fiber obtained from waste paper, there is a need in the industry to develop a process that is more efficient and cost effective.